Findings released yesterday will have a "profound" effect on the way Hastings' drinking water is treated in the future, possibly starting with up to $6 million spent on UV treatment.
Yesterday Hastings District Council released a report from GNS Science, which revealed water - some as young as a month old - had been found in its bores.
In secure supplies older water is desired, as contamination in the form of living organisms cannot survive in the ground for long periods.
The report was commissioned by the council as part of the five-yearly assessment of the district's water supplies under the New Zealand Drinking Water Standards, and was based on water samples taken in May.
Until August, all water sources for Hastings' urban supply were classified as "secure" under these standards.
In the midst of the Havelock North water contamination crisis in August - which saw 5200 people become ill - GNS released findings revealing there was potential for young water to be found in a number of bores.
The results released yesterday showed a significant proportion of young water in samples drawn from the Brookvale and Wilson Rd bores, and pointed to possible young water being drawn from the Frimley Bore.
In Brookvale, the youngest water found was just over a month old, meaning it had the potential to introduce bacteria into the water source.
The results could make it difficult for a number of the council's water sources to be classified as secure under the drinking water standards.
Hastings mayor Lawrence Yule said if there had been no new water found, continued chlorination, or no treatment of water supplies would have been an option.
"We now know that even with chlorine in that will not be enough, because of these reports, to meet the New Zealand Drinking Water Standards for those bores," he said.
It would have cost the council between $50,000 and $100,000 a year for chlorination, as it already had the system in place.
Now, the council would have to consider implementing UV treatment across the entire urban network to ensure it complied with the standards. This could cost between $4 to $6 million in capital costs.
When asked if this would mean a rates increase, Mr Yule said the council had not worked out how this would be covered, "but it's going to be another $5 or $6 million that has to be spent as a significant cost on the ratepayer".
Mr Yule said he was unsure about a timeline for this. "These results are profound for the way in which we'll treat Hastings drinking water, and will have significant impacts," he said.
"Because up until now we've deemed that the aquifer water is secure, with the influx of new drinking water it now does not meet that test."
The council had asked the GNS Science team whether young water in the samples could have been caused by a leak or fault in the bores themselves.
The scientists had believed this was unlikely, and advised council the tests were not sensitive enough to pick up such small quantities of water.
Mr Yule said this testing confirmed across other parts of the Heretaunga plains there was new water getting in to the aquifer.
In a statement, the district council said the report indicated the biggest presence of young water in the aquifer system was in the "unconfined" areas of the aquifer. T
he core Heretaunga Plains aquifer still provided pure and clean water.
Mr Yule said the report's implications showed where old river terraces intercepted on the Heretaunga plains, and there were bores in that area, there appeared to be a much greater amount of young water than present there five years ago.
"That is a serious issue for everybody, for all users, because something has changed," he said.
"Clearly what it means is that for the first time we can now show it is new [water], something has dramatically changed in the aquifer and there is new water entering what were traditionally very secure supplies."
The council was currently assessing the implications of the report, and had provided a copy to the Hawke's Bay Regional Council (HBRC) "to assist it in its responsibilities for managing the region's groundwater resources".
HBRC stated the suggestion the Havelock North contamination might have been caused by aquifers it was responsible for was ruled out by a team of around 15 scientists - half who were external - who investigated the cause.
HBRC chief executive Andrew Newman said HBRC comprehensively tested to determine if the aquifer was the source of the contamination, and found it was not.
"The results are all in the Investigation report. The testing and peer review of the report by experts has been given to the Government Inquiry into the Havelock North Water Contamination Inquiry," he said.
Mr Newman said as the Heretaunga aquifer was vast, and with varying depths it would have varying ages of water.
"So there's nothing unusual about that per say and nothing of great surprise. I guess it depends on what water is used for, under what circumstances whether it is an issue or isn't an issue."
HBRC was undertaking a significant piece of work on the aquifer in its entirety under the TANK process.
The GNS report had found across the aquifer system, the average water age seemed to be getting younger, with 'mean residence times' reducing.
The council stated this could suggest levels of water abstraction - the taking of water from the aquifer for irrigation, industrial use, municipal water supply and other purposes - might be having an influence on the aquifers "although further testing would be required to confirm this".
When asked about this, Mr Newman said, "That's true, well put it this way, that is a possible issue absolutely".
Tukituki MP Craig Foss said he hoped what these results showed were investigated scientifically "for all the right reasons, rather than part of this council vs council which the ratepayers are paying twice for".
Mr Foss said he had been hearing various reports along the lines of the one released yesterday, but not as young as the water found in these results.
"At the end of the day we need to turn on our taps we need to be able to drink the water safely and trust in the processes around it full stop.
"Sadly this kind of seems to add into the murky water around all the water issues and I sincerely hope for ratepayers as well as being a local MP this is sorted out pretty quickly".
There would be a press conference held on Monday about various water issues.
Hastings District councillors attended a workshop yesterday to get an update on water supply issues which prompted a sprinkler ban on Thursday last week.
The pressure on the water resource had already reached a five-year peak last weekend, and throughout the week pumps drawing water from the aquifer into reservoirs feeding Hastings, Havelock North and Flaxmere have struggled to keep up with demand.
Mr Yule did not attend the workshop yesterday but said the aim was to update councillors on issues such as reservoir levels, how the council was dealing with leaks, and progress being made readying Brookvale bore 3 to be re-activated as an additional water supply source.
Councillor Simon Nixon said the workshop was useful for councillors to be informed when ratepayers asked them questions.
He believed the council was doing everything that it practically could to minimise inconvenience and maximise the water available.
The re-activation of the Brookvale bore, along with the other two bores there, was subject to the approval of the Government inquiry investigating the Havelock North water contamination event in August, Mr Yule said.
This inquiry had been delayed due to the Hawke's Bay Regional Council laying charges against the Hastings District Council for the unlawful taking of water.
"Because the rest of the inquiry has been delayed, the inquiry team has said it's important to sort this bore out for the summer and they have brought it forward as a priority," Mr Yule said.
This was now due to be considered at a public hearing at the Hastings District Court on December 12 and 13 when the inquiry's focus would be on actions and further actions to ensure a safe supply of drinking water to Havelock North over the next 12 months.